VUV Spectrometer Using Prism Dispersion and Toroidal Mirror
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Solution Overview
Problem
Current optical spectroscopy instruments face challenges in achieving high efficiency and moderate resolution in the vacuum ultraviolet (VUV) region due to low reflectivity of metals, astigmatism, and complex wavelength dependencies, making it difficult to design compact systems for commercial applications.
Innovation Solution
A compact VUV spectrometer using a single pass prism configuration with a fast off-axis parabolic mirror and a LiF prism, which separates and disperses light into a flat field focal plane suitable for array detectors, reducing the number of optical surfaces and minimizing contamination effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard reflection gratings with Al coating are used in VUV, then reflectivity is enhanced over wide wavelength range, but oxidation of aluminum films drastically reduces reflectivity at wavelengths lower than 170 nm
Solution Approach 1:
The patent applies composite coating structure with MgF2 overcoat on Al film. The MgF2 layer serves as a protective barrier against oxidation while maintaining optical performance in the VUV region, resolving the contradiction between enhanced reflectivity and oxidation resistance.
2Reliability
If concave gratings are used to eliminate reflective surfaces, then VUV efficiency is improved, but astigmatism results in loss of intensity and spatial resolution
Solution Approach 1:
The patent employs a toroidal mirror with specific curvature radii (R1 and R2) to focus dispersed light onto a flat focal plane. This curved surface design corrects astigmatism by providing different focal lengths in orthogonal directions, maintaining both VUV efficiency and spatial resolution.
3Measurement precision
If finely ruled gratings are used to achieve high spectral resolution, then resolution is improved, but VUV efficiency profiles are low and exhibit complicated wavelength dependencies
Solution Approach 1:
The patent changes the optical configuration from grating-based to prism-based dispersion, utilizing refractive index variations with wavelength instead of diffraction. This parameter change achieves moderate spectral resolution with high and flat VUV efficiency across the spectrum, avoiding the efficiency losses and wavelength dependencies of finely ruled gratings.
4Reliability
If grazing incidence grating mounts are used to overcome low normal incidence reflectivity, then VUV efficiency is improved, but the systems require large focal lengths and do not lend themselves to small footprint instruments
Solution Approach 1:
The patent uses a toroidal mirror with specific curvature radii to achieve focusing in a compact configuration. The curved surface enables short focal length operation while maintaining high VUV efficiency, allowing small footprint instrument design without sacrificing optical performance.
5Adaptability or versatility
If multiple optical surfaces are used in the light path, then dispersion and focusing capabilities are achieved, but contamination effects increase in the VUV region
Solution Approach 1:
The patent extracts the dispersion function from the focusing optic by using a separate prism for wavelength separation. This functional separation reduces the number of optical surfaces in the main light path, minimizing contamination effects while maintaining both dispersion and focusing capabilities.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides high throughput and improved alignment tolerance, enabling efficient moderate resolution spectroscopy in the VUV region with reduced stray light and chromatic aberrations, suitable for commercial instruments and metrology applications.
Implementation Method 1
at least one optical element which receives light from the light source after it passes through the entrance port, the light received by the at least one optical element being collimated, the optical element separating the received collimated light into multiple spatially separated wavelengths of light
Implementation Method 2
a first off-axis parabolic mirror which receives the light from the collimated light source and focuses the light onto a focal plane
Data Source
AI summary
An optical spectroscopy tool is provided. In one embodiment a highly efficient means by which moderate resolution spectroscopy may be performed in the vacuum ultraviolet (VUV) is described. In one embodiment the techniques can be used as a high throughput spectrometer to spatially disperse wavelengths in and around the VUV in such a manner as to generate a substantially flat field focal plane, suitable for use in combination with an array detector. Some embodiments utilize prism based spectrometers. Some embodiments utilize detector elements that may be movable and/or located within the spectrometer. In some embodiments, collimated light may be provided as an input to the spectrometer.